1. Field of the Invention
This invention relates generally to video cameras. More particularly, the invention relates to a method and apparatus for white balancing a color video camera.
2. Background of the Invention
When white balance is not correctly adjusted in a color video camera, the image taken by the color video camera may have reddish or bluish hue. Therefore, adjustment of white balance is very important.
There are several ways to obtain white balance data necessary to perform a white balancing process. In a first technique, the video signal is integrated over one whole image. In a second technique, the image is divided into plural regions and the video signal in each region is respectively integrated. In a third technique, the brightest portion (presumed to be a white object) in an image is detected. Adjustment of white balance is done based on the data obtained by the above described methods.
However, under the first method, when an image includes a large colored object like a uniformly green lawn, the adjustment of white balance includes adjustment error due to the effects of the large colored object. Under the second method, if there are no white objects in the regions, adjustment error can occur. Under the third method, if the image includes a TV screen, outdoor light from a window or bright sunlight at sunset, error can also be introduced into the white balance adjustment. When an image includes both bright sunlight and shade at the same time, the blue of shade is emphasized too much because the adjustment tends to make the bright sunlight portion white.